This invention relates to a method and apparatus for electrical measurement of the rate of a flow of liquid or gas.
In internal combustion engines, an intake system usually includes a fuel metering device or an air-fuel proportioning device such as a carburetor or an electronically controlled fuel injector to feed the engine with an air-fuel mixture of a predetermined air/fuel ratio. In recent years, there is a strong and growing demand for improvement on the precision in the control of the air/fuel ratio particularly in automotive internal combustion engines, since the improvement is almost a requisite to the success in reducing harmful components of the exhaust gas and lessening the fuel consumption to the extent of fully meeting current requirements without substantial sacrifice of the operability of the engines.
To maintain the air/fuel ratio exactly at a predetermined value, there is a need of precisely adjusting the fuel supply rate to changes in the quantity of air being admitted into the engine. Accordingly there is a great need for the development of improved measuring instruments which are high in precision, good at response and are really adapted to measurement of volumetric flow rates of air and liquid fuel in intake systems of automotive internal combustion engines.
Conventional flow rate measuring instruments are generally unsuitable for use in association with automotive internal combustion engines, for example as a component of a carburetor, mainly from the following reasons. First, their responsiveness is insufficient to follow such transient variations as occur in the flow rate of air and/or fuel in automotive engine intake systems. For example, a flow meter of the so-called burette type, in which a rotatable or swingable measure is cyclically filled with a flowing fluid and emptied to represent the rate of the flow by the amount of time taken by one cycle of this work, cannot detect a momentary flow rate but can only indicate an average flow rate during 10-60 seconds. Second, they are generally large in size, heavy in weight and, because of having mechanically moving parts, complicated in structure.